Method of forming resist pattern on substrate

ABSTRACT

A method of forming resist pattern is disclosed. After the resist pattern is formed, an ion beam is irradiated on the resist pattern. The energy of the ion beam is controlled in every segments of the resist pattern by a predicted deviation data stored beforehand, so that the unfavorable deviation of the resist pattern is minimized.

BACKGROUND OF THE INVENTION

The present invention relates to a method of forming a resist pattern ona substrate, and more particularly, to a method of forming a resistpattern on a metal layer provided on a glass substrate to produce a maskfor manufacturing a semiconductor device.

The resist pattern is widely used in the field of semiconductor device.For example, the mask for manufacturing the semiconductor device isproduced by following process steps: depositing a metal layer such as achromium layer on a major surface of the glass substrate, coating aresist film on the metal layer, selectively exposing the resist film byan electron beam, etc., developing the resist film to form the resistpattern, and selectively etching the metal layer by using the resistpattern as an etching mask. On the other hand, in the manufacturingprocess steps for the semiconductor device, the resist pattern is formedon a conductive layer such as a polycrystalline silicon layer or analuminum layer or on a insulating layer provided on a semiconductorsubstrate, that is, a semiconductor wafer, and selectively etching theconductive layer or the insulating layer by using the resist pattern asan etching mask to form electrode wirings or contact holes. In anycases, a precise resist pattern is necessary over the entire area.

However, even if the resist pattern has a precise and designed dimensionat one portion, at other portions on the same substrate, the dimensionsof the resist pattern are inevitably deviated to some extent from thedesigned value. The deviation is caused by the previous process steps ofcoating the resist film, selectively exposing the resist film anddeveloping the resist film. If many specimens (mask substrates orsemiconductor wafers) are treated in substantially identical apparatusand with substantially identical conditions in each process step, thespecimens have the same distribution of the deviation in the resistpattern over the entire areas, each other. For example, if the resistpattern of one specimen becomes 0.2 μm broader than the designed valueat one portion, the other specimens have the same tendency that therespectively resist patterns become about 0.2 μm broader at thecorresponding portions. In the prior art, more precise resist patternover the entire areas cannot be obtained. To realize a high integratedsemiconductor device having a fine pattern, the deviation of thedimension in the resist pattern must be compensated over the effectiveareas of the substrate entirely.

SUMMARY OF THE INVENTION

Accordingly, an object of the present invention is to provide a methodfor forming resist pattern on a substrate in which the unfavorabledeviation of the resist film can be minimized.

According to the present invention, the method comprises steps offorming a layer to be selectively etched on one major surface of asubstrate, coating the surface of the layer with a resist film,selectively exposing the resist film, developing the resist film to forma resist pattern, and irradiating an ion beam on the resist pattern, theenergy of the ion beam being changed at every segment areas of theresist pattern on the basis of predicted deviation distribution data ofthe resist pattern caused by the previous process steps so that thedeviation of the resist pattern by the previous process steps iscompensated and minimized. The previous process steps include coatingthe resist film and developing the resist film. When an electron beamexposure is employed. The selectively exposing process step is furtherincluded in the previous process steps. The layer to be selectivelyetched by using the resist pattern as an etching mask may by a chromiumlayer and/or a chromium oxide layer and the substrate may be a glassplate transparent to UV light or soft-X-rays of a mask for manufacturinga semiconductor device. The layer may be a conductive layer made ofpolycrystalline silicon, aluminum, etc. or an insulating layer made ofsilicon oxide, silicon nitride, etc., and the substrate may be asemiconductor wafer such as a silicon wafer. Further, the substrate is amembrane including, for example, an insulating film such as a siliconoxide film and/or a silicon nitride film of a mask for X-raylithography.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A to 1G are cross-sectional views showing process steps insequence according to an embodiment of the present invention;

FIG. 2 is a plan view showing a mask which is conducted an electron beamexposure on the resist film;

FIGS. 3A and 3B are tables showing the deviation of the resist patternwidth W₁ in one field, respectively, caused by the process step ofselectively exposing the resist film by an electron beam exposure;

FIGS. 4A and 4B show the deviation of the resist pattern width W₁ inadjacent four fields, respectively, caused by the process step ofselectively exposing the resist film by the electron beam exposure;

FIGS. 5A and 5B are tables showing the deviation of the resist patternwidth W₂ in an entire area of one mask, respectively, caused by processsteps of coating and developing the resist film;

FIGS. 6A and 6B show the deviation of the resist pattern width W₂ in onemask, respectively, caused by process steps of coating and developingthe resist film;

FIG. 7 shows a predicted deviation distribution of the resist patternwidth W caused by the previous process steps including selectivelyexposing the resist film by the electron beam exposure, coating theresist film and developing the resist film;

FIG. 8 is a schematic cross-sectional view showing the compensation ofthe deviation of the resist pattern width by an ion beam irradiation;

FIG. 9 is a schematic view including a block diagram showing aprocessing equipment employed in the present invention; and

FIG. 10 is a graph showing the relation between an amount of removedwidth of the resist pattern width by the ion beam irradiation and an ionaccelerating voltage of the ion beam.

EMBODIMENT OF THE INVENTION

Referring to FIGS. 1A to 1G, a method of manufacturing a photo-maskaccording to the present invention is disclosed. A chromium layer 2 isdeposited on a major surface of a glass substrate 1 (FIG. 1A), and onthe chronium layer a resist film 3, for example, OEBR-100 made by TokyoOhka Kogyo Co., Ltd. having the thickness of 6000 Å is coated by aspin-coating method (FIG. 1B). The resist film 3 is subjected toselective exposing of an electron beam (e⁻) 5 (FIG. 1C), and thereafterthe resist film 3 is developed to form resist patterns 3a, 3b where theelectron beam has been irradiated (FIG. 1D). Each of resist patterns 3a,3b deviates its plan shape from the designed value, and a minute resist4 remains unfavorably between the patterns. The deviation of the resistpattern is caused by the selectively exposing process step by anelectron beam, the coating process step and the developing process step.Then, as shown in FIG. 1E, a Ga⁺ ion beam 6 is irradiated on the resistpatterns 3a, 3b. The energy of the ion beam 6 is control by a predicteddeviation distribution data and changed its energy in respectiveportions on the substrate. For example, when the resist pattern on oneportion is predicted to be 0.1 μm wider than the designed value, theenergy is control to remove the side surfaces and the upper surface ofthe resist pattern by 0.05 μm. On the other hand, if the resist patternon other portion is predicted to be 0.2 μm wider than the designedvalue, the energy, that is, the accelerating voltage is changed to ahigher level and the resist pattern is removed at side and uppersurfaces thereof by 0.1 μm. During the ion beam irradiation process, theremaining minute resist 4 can be completely removed. Thereafter, thechromium layer 2 is selectively etched by using the compensated resistpatterns 3a', 3b' as an etching mask to form metal patterns 2a, 2b (FIG.1F), and by removing the resist patterns 3a', 3b', a photo-maskincluding the transparent glass plate 1 and the opaque metal patterns2a, 2b can be completed (FIG. 1G).

Referring to FIG. 2, when the electron beam exposure is employed in theselectively exposing the resist film 3 on the substrate 1, the entirearea is divided into a plurality of small areas 10 (hereinafter calledas field). In FIG. 2, each field 10 has the 2 mm×2 mm size and it can beregarded, for example, as one chip area of the semiconductor device.Each of fields is set, in sequence, under an electron beam system by anX-Y stage on which the mask substrate 1 is installed. When one field issubjected to the selective exposure, the X-Y stage stops its movementand the electron beam is scanned within the field area (2 mm×2 mm) bythe deflection system. At the center part of the field, the electronbeam is irradiated along a passage normal to the surface of the resistfilm, and at the peripheral part of the field, it is irradiated along apassage inclined from the normal passage. Therefore, the exposureconditions at the center part and the peripheral part become inevitablydifferent. If the condition at the center part is set to obtain thedesigned value, the condition of the peripheral part cannot be optimizedand the resist pattern therein deviates from the designed value. Thedeviation of the resist pattern caused by the electron beam exposuredepends on the electron-beam scanning within one field as mentionedabove. Therefore, any fields in any masks treated in an identicalapparatus can be expected to have the same tendency of the deviation.FIGS. 3A, 3B, 4A and 4B show the examination results of the resistpattern width deviation caused by the electron beam exposure. FIGS. 3Aand 4A are of the same one mask, and FIGS. 3B and 4B are of thedifferent one mask. In FIGS. 3A and 3B, each field 10 is divided into 25segments 11 of 0.4 mm×0.4 mm, and in the respective segments 11 thewidth W₁ are estimated. In FIGS. 4A and 4B, the resist pattern widths W₁are vertically shown in adjacent four fields 10, respectively. Clearlyfrom these FIGS. 3, 4, the substantially equal tendency of the deviationby the selective exposing process step in each field can be confirmed.

By a spin-coating of the resist film in which the resist is dropped atthe center of the substrate and the substrate is rotated at 1000 to 5000rpm, the thickness of the resist film at the peripheral portion of thesubstrate becomes thicker than that of the center portion of thesubstrate by 100 to 500 Å in any substrates. By a spray-type developingin which the substrate is rotated at 100 to 1000 rpm and the developeris sprayed on the resist film, the development condition at theperipheral portion of the resist film differs from the developmentcondition at the center portion thereof. However, the difference cankeep the substantially same tendency among a plurality of substrates(makss) if they are treated in an identical apparatus. Therefore, thedeviation of the resist film pattern caused by coating and developingprocess steps of the resist film can be expected to have the sametendency among a plurality of masks. Referring to FIGS. 5A, 5B, 6A and6B, the examination results of the resist pattern width deviation causedby coating and developing process steps are shown. FIGS. 5A and 6A areof the same one mask, and FIGS. 5B and 6B are of the different one mask.In FIGS. 5A and 5B, the pattern widths W₂ are examined at one point inevery fields 10. The point at which the width is examined in each field10 is located at the same position in each field to reject the influenceof the exposing process step mentioned above. In FIGS. 6A and 6B, theresist pattern widths W₂ are vertically shown in a part of therespective mask specimens 1. Clearly from these FIGS. 5, 6, thesubstantially equal tendency of the deviation by the coating anddeveloping process steps in each mask specimen can be confirmed.

A predicted deviation data P_(V) of the resist pattern can be obtainedby combining the experimental data of FIG. 3 and the experimental dataof FIG. 5. In this case, the resist pattern over the effective substratearea is divided to 625 (25×25) segments 11 (FIG. 2), and in each segment11, one predicted deviation datum is provided, though not shown inTable. That is, the predicted deviation data P_(V) includes 625predicted deviation values. The ion beam is irradiated with a constantenergy, that is, a constant accelerating voltage within one segment, andchanged its energy, if necessary, when the other segment is irradiated.Referring FIG. 7, the predicted deviation distribution data P_(V) of theresist pattern, that is, the predicted widths W, which are verticallyshown, at respective portions of the substrate is exemplified. Thepredicted deviation data P_(V) is used to control the acceleratingvoltage of the ion beam irradiating respective portions, when an actualspecimen, that is, an actual mask or an actual semiconductor device isproducted.

Referring to FIG. 8, if the predicted width W is 4.2 μm at the portion40, the practical pattern 50 would be also of 4.2 μm width. Therefore,the ion beam is enhanced its energy at the portion 40 and the upper andside surfaces thereof are removed by the ion beam by 0.1 μm, that is,1/2 ΔW is 0.1 μm so that a resist pattern 50' having the designed widthof 4.0 μm is obtained at the portion 40. The ion beam scanned or movedfrom the portion 40 to portion 41. If the predicted width W is 4.1 μm atthe portion 41, the practical pattern 51 would be also of 4.1 μm width.When the ion beam is positioned at the portion 41, the energy isdecreased so that the side and upper surfaces of the resist pattern 51are slightly removed by 0.05 μm, that is, 1/2 ΔW is 0.05 μm and theresist pattern 51' having the design width of 4.0 μm is obtained. Forexample, when Ga⁺ ion beam of 0.5 A/cm² and 1 μm φ diameter is scannedat the speed of 350 mm/sec, if the accelerating voltage of the ion beamis changed from 40 KV to 60 KV, the removed width (ΔW) of the resist canbe changed from 100 Å to 1000 Å.

Referring to FIG. 9, the equipment of the ion beam processing equipmentused in the present invention is shown. An ion generation chamber 83 isconnected to a gas supplying chamber 81 and to a vacuum chamber 84.Outside the ion generation chamber 82, an ion generation power supplyand its electrode 82 are installed. A vacuum pump 85 is coupled to thevacuum chamber 84, and in the vacuum chamber 84, an acceleratingelectrode 80, a focusing electrode 86, a blanking electrode 87, adeflection electrode 88 and an X-Y stage 89 installing the masksubstrate are provided. An ion beam 90 from the chamber 83 is irradiatedon the resist patterns 3a, 3b on the substrate 1 through the electrodes80, 86, 87, 88. The electrode 80 is connected to an accelerating voltagepower source 91 controlled by an accelerating voltage control section 96and the focusing electrode 86 is connected to a focusing voltage powersource 92 controlled by a focusing voltage control section 97. Theblanking electrode 87 is connected to a blanking voltage power source93, and the deflection electrode 88 is connected to a deflection voltagepower source 94. The X-Y stage 89 is moved in X and Y directions by apair of motors 95 each controlled by a stage control section 98. Theaccelerating voltage control section 96, the focusing voltage controlsection 97, the blanking voltage power source 93, the deflection voltagepower source 94 and the stage control section 98 are coupled to aconverting unit 99 which is coupled to a data input unit 100. Apredicted deviation resist pattern width data P_(V) is input to the datainput unit 100, and in which the data is normalized on a basis of theminimum width value being zero. The normalized data is sent to theconverting unit 99. In the converting unit 99, the optimum acceleratingvoltages in respective portions are estimated by the normalized data anda relation between an accelerating voltage and an amount of the removalof the resist shown in FIG. 10 stored in the converting unit 99beforehand. The estimated data is sent to the accelerating unit 96 whichcontrols the accelerating voltage power source 91 by the estimated datato supply optimum voltages to the accelerating electrode 80corresponding to the every portions of the ion beam 90 on the resistpatterns. Also, best focusing conditions are obtained in the respectiveaccelerating voltage levels by the focusing voltage control section 97,the focusing voltage power source 92 and the focusing electrode 86. Theion beam 90 is scanned within one segment 11 (FIG. 2), for example, onthe substrate by the deflection electrode 88, and after scanning withinone segment, the substrate 1 is moved by the X-Y stage 89 so that thenext segment 11 is positioned under the ion beam.

Turning to FIG. 2, the predicted deviation data of the resist patternare provided against respective small segments 11. Therefore, in eachsegment 11 of 0.4 mm×0.4 mm, the ion beam is scanned with a constantvoltage (constant energy), and after scanning the ion beam within onesegment 11, the voltage of the ion beam is changed, if necessary, andthe substrate is moved by the X-Y stage so that next segment 11 ispositioned under the ion beam 90 thereby conducting the ion beamscanning on the next segment with the changed constant voltage. Then alleffective areas of the resist pattern consisting of 625 segments in theembodiment are irradiated by the ion beam which varies its energy inevery segments so that the deviation of the resist pattern in eachsegment from the designed value is minimized. In the embodiment, thewidth of the resist stripe in the resist pattern has been in problem.However, the present invention is also useful when an interval widthbetween resist stripes is in problem. In this case, the interval widthbecomes broader by irradiating the ion beam. Further, the presentinvention is useful in any kinds of resist, in positive type or negativetype, for example. Moreover, the size of the segments 11 can be changed,if necessary.

What is claimed is:
 1. A method of forming resist pattern on a substratecomprising steps of forming a layer to be selectively etched on onemajor surface of a substrate, coating the surface of said layer with aresist film, selectively exposing said resist film, developing saidresist film to form a resist pattern, and irradiating an ion beam onsaid resist pattern, the energy of said ion beam being changed at everysegment areas of said resist pattern on the basis of predicted deviationdistribution data of the resist pattern so that the deviation of saidresist pattern is minimized.
 2. A method of claim 1, in which saidpredicted deviation distribution data is obtained by examination resultsfor the deviations in a resist pattern caused by coating and developingsaid resist film.
 3. A method of claim 1, in which said predicteddeviation distribution data is obtained by examination results for thedeviations in a resist pattern caused by coating, selectively exposingand developing said resist film.
 4. A method of claim 3, in which saidselectively exposing said resist film is conducted through an electronbeam exposure method.
 5. A method of claim 1, in which said layer ismade of metal and/or metal oxide to form an opaque pattern of a mask,and said substrate is a glass substrate of said mask.
 6. A method ofclaim 1, in which said layer is made of conductive material, and saidsubstrate is a semiconductor wafer.
 7. A method of claim 1, in whichsaid layer includes an insulating layer, and said substrate is asemiconductor wafer.
 8. A method of claim 1, in which said substrate isa membrane of a mask for X-ray lithography.